Cotton is the world's leading textile fiber and it is grown on over six million hectares in the United States (US) (USDA-National Agricultural Statistics Service, 2005). Cotton is one of the leading cash crops in the U.S. Cotton fiber generates in excess of $6 billion per year, while cottonseed oil and meal add another $500 million per year to the total US agricultural economy. More than 440,000 domestic jobs are created by cotton production and processing which has a total impact of over $40 billion on the US gross domestic product (National Cotton Council 2005). U.S. cotton exports also contribute about $2 billion per year to our trade balance.
Cotton has been selected and cultivated primarily for its fiber. Although the seed now is used in the production of oil, meal, and dairy feed, its economic value to the modern farmer for these uses is low in comparison to the economic value of the fiber, which is used to produce yarn, fabric and textile garments. Despite the greater mass per acre of seed as compared to fiber, the even greater economic value per pound of fiber as compared to seed has encouraged plant breeders to select cotton primarily for increased fiber yield and fiber quality, and only secondarily for increased seed yield and seed quality. As a result of this intense selection for genetic improvements in fiber yield, the genetic contribution to fiber yield and lint percent has increased during the last 50 years while seed size has declined.
The 1.3 billion pounds of cottonseed oil produced each year make it the third leading vegetable oil in the U.S. The cottonseed industry is a $1.2 billion industry and has historically provided up to 15% of the gross return on cotton production. Thus, there is a need to increase the yield of cottonseed oil as well as cotton fiber yield and fiber quality, while simultaneously reducing the cost of producing these commercially important products.
Nearly 20% of the U.S. total cotton production (three million bales) occurs on the High Plains of Texas. Because of the relatively poor fiber quality of the cultivars adapted to this short growing season region, this cotton has historically been sold to low value markets. Currently, there is a need to improve cotton fiber quality and seed oil content and to reduce the cost of production for the cotton cultivars adapted to this region. Studies have been conducted to determine the inheritance of improvements in fiber quality in cotton. There is a need to develop cotton seed mutants which have the potential to improve fiber quality without introducing alien genes that may reduce adaptation to production regions having a short growing season.
Ideally, the incorporation of such traits into well-adapted commercial cultivars would speed up and reduce the cost of ginning, reduce the need for delinting cotton seed used for planting, increase seed oil content, reduce the need to remove linters prior to oil extraction, and improve cotton fiber quality by reducing seed coat neps and short fiber content, thus maximizing the economic value and commercial utility of cotton crops.
The use of chemically-induced mutants has been highly successful in most major crops grown across the world but has only occasionally been used in improving cotton (Auld et al., 1998). However, the relatively low level of genetic variability currently available in cotton would indicate this would be an ideal tool to increase genetic variability in this species. Mutagenesis has been shown to be an effective tool to create a wide range of phenotypic variation in both diploid and tetraploid Gossypium populations (Auld et al., 2000; Larik et al., 1983; Gaibullaev et al., 1976; Hussein et al., 1982 and Shattuck and Katterman, 1982). The creation of these new mutants is a powerful tool for both functional genetics and conventional genetic improvement of cotton.
The cotton cultivars adapted to the High Plains of Texas, unlike commercial upland cotton, have a narrow germplasm base that has limited the success of breeding programs attempting to improve fiber quality using conventional breeding techniques. Recent studies at Texas Tech University indicate successful mutagenesis in cotton from exposure of germinating embryos to high rates of ethyl methanesulfonate (EMS). These studies of mutant lines reveal significant potential for improvement of fiber quality in cotton. Such developmental studies using chemical mutagenesis for inducing heritable variation in cotton fiber quality show promise for cotton markets where fiber quality is at a premium.